The view pg_group exists for backwards
compatibility: it emulates a catalog that existed in
PostgreSQL before version 8.1.
It shows the names and members of all roles that are marked as not
rolcanlogin, which is an approximation to the set
of roles that are being used as groups.
Table 42-35. pg_group Columns
|groname||name||pg_authid.rolname||Name of the group|
|grosysid||oid||pg_authid.oid||ID of this group|
|grolist||oid||pg_authid.oid||An array containing the IDs of the roles in this group|